秸秆生物质炭与水分管理对稻田铬形态及水稻铬积累的协同影响及其生物化学机制

The behavior of chromium is related to its chemical forms. Reduction-oxidation reactions are important processes affecting chromium transformation. Organic matter and ferrous iron are the most common reductants involved in the reduction of hexavalent chromium in paddy soils. Derived from pyrolysis of straw at high temperature and low oxygen content, biochar is believed to have huge potential on soil organic matter improvement. Water management is an important factor affecting ferric iron reduction and ferrous iron oxidation in paddy soils. However, the synergistic effects of straw biochar and water management on chromium transformation and their mechanisms are still unkown. In the proposed work, the synergistic effects of straw biochar and water management on chromium transformation will be illuminated on soil chemistry and microbial ecology. The variations of oxygen, redox potential, pH, DOM in rhizosphere soils under different biochar application levels and water managements, and their relationships with the variations of iron redox cycling and chromium transformation will be determined. The coupling relationship between iron redox cycling and chromium transformation in the rhizosphere soils will be evaluated to illuminate the mechanism of iron redox cycling regulating the reduction of hexavalent chromium in paddy soil and thus chromium accumulation in rice. The functional microbial populations participated in the reduction process of ferric iron and hexavalent chromium will be identified to reveal microbially-mediated mechanism of iron redox cycling and chromium reduction. Moreover, the character and element content of biochar will be determined to reveal the interaction mechanisms between straw biochar and soil iron and chromium transformation. The purpose of this project is to reveal the synergistic effects of straw biochar and water management on chromium transformation and accumulation and their biochemical mechanism, and optimize the management practices to reduce chromium ecological risk for ensuring the safe production of rice.

铬的环境行为主要取决于铬的存在形态，氧化-还原作用是影响铬存在形态的重要因素。稻田土壤中有机质和亚铁是铬还原最主要的还原剂。来源于秸秆高温厌氧炭化的生物炭，在提升土壤有机质方面极具潜力。水分管理方式是影响稻田氧化铁还原和亚铁氧化的重要因素。但秸秆生物质炭与水分管理对稻田铬形态转化的联合效应尚不明晰。本申请拟从土壤化学、微生物学角度，研究不同秸秆生物质炭施用水平、不同水分管理下水稻根际溶氧量、Eh、pH、DOM动态对铁循环及铬形态转化的影响；判定根际土壤铁循环与铬形态转化之间的耦合关系，阐明铁循环耦合调控铬还原转化的作用机制；明确介导铁、铬还原的功能微生物种群，探明铁循环耦合调控铬还原转化的微生物驱动机制；揭示生物质炭与土壤铬、铁元素之间相互作用机制。该研究可探明秸秆生物质炭与水分管理对稻田铬形态及水稻铬积累的协同影响及其生物化学机制。为找到有效的生产管理方式降低稻田铬生态风险提供科学依据。

铬的环境行为主要取决于铬的存在形态，氧化-还原作用是影响铬存在形态的重要因素。本项目从土壤化学、微生物学角度，研究不同秸秆生物质炭施用水平、不同水分管理下水稻根际Eh、pH、DOM动态变化，以及对铁循环及铬形态转化的影响；并分析了根际土壤铁循环与铬形态转化之间的耦合关系，阐明了铁循环耦合调控铬还原转化的作用机制；同时研究了介导铁、铬还原的功能微生物种群，阐明了铁循环耦合调控铬还原转化的微生物驱动机制。主要结果及数据如下：（1）生物炭的添加显著降低土壤氧化还原电位，并相应提高了土壤pH。淹水条件下土壤处于厌氧还原状态，且氧化还原电位随时间呈下降的趋势，而干湿交替条件下土壤在氧化和还原状态之间反复波动。（2）生物炭的添加显著提高了土壤可溶性有机质含量。（3）生物炭和淹水处理协同促进了土壤中六价铬还原为三价铬。（4）生物炭和淹水处理协同降低了土壤中铬的迁移能力和稻米中铬的含量。（5）淹水条件下根系表面形成的铁膜可以吸附固定土壤溶液中的铬离子，并成为铬离子进入根系组织的阻碍层，降低水稻对铬的吸收累积。（6）不同生物炭和水分管理方式下土壤pH和氧化还原电位改变导致土壤微生物群落组成、多样性、功能基因构成都发生显著变化。这些成果为在铬污染稻田安全栽培水稻提供理论依据和科学支持。